How to Choose a Roofing Underlayment for Your Home

By Ben Matthews | Mar 18, 2016 11:00:00 AM

Though they are rarely seen, roofing underlayments are a crucial part of any roof. Unless you're a roofing professional, however, you may not even know what an underlayment is, much less how to choose the right one for your home. So what exactly is the role of underlayment? And how do you pick which one to install?

The Importance of Underlayment

When your roof is constructed, it is built in stages. The first layer of your roof, the deck, is the surface you see when you climb into your attic. It forms the backbone of the roof and is where all the other pieces are attached. The top layer of the roof is the shingle, which forms the main protective barrier against the elements. But between those two layers lies a third: the underlayment


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Underlayment is a semi-breathable membrane made of any of several different materials. Its purpose is to provide a second layer of protection against water intrusion and leaks, while also allowing air and humidity to escape from the roof deck below. Underlayment helps preserve and protect the roof deck, and it also creates a watertight seal where shingles and flashing are tacked or nailed in.

Most underlayment used in modern homes is made of asphalt-saturated felt. This material has many good qualities and is easy to work with on almost any type of roof. However, many homeowners are also choosing to use non-bitumen synthetic underlayment, which has a number of advantages as well. So which one is right for you?

Choosing a Roofing Underlayment

There are many differences between felt underlayment and synthetics. In general, felt underlayment is:

  • Less expensive than synthetic underlayment.
  • Thicker and heavier than synthetic.
  • Somewhat less durable than synthetic, though this can vary based on the type of felt used.
  • More prone to water absorption and wrinkling over time than synthetic.
  • Less weather-resistant on its own - your roofer should begin installing shingles immediately once they install a felt underlayment.

In contrast, synthetic underlayment, in general, is:

  • Somewhat more expensive, though there are several grades of synthetic underlayment to choose from to help you balance expenses and performance.
  • Lighter and easier to move around than felt.
  • More durable and long-lived than most felt.
  • Less prone to wrinkling and rotting than felt (since it doesn't use any organic fibers).
  • More weather-resistant in its own right than felt.

So which one should you choose?

Many homeowners choose felt because it is a familiar and tested material. Felt works well in a variety of roofing applications and provides a good barrier for your roof deck for many years. A well-installed layer of No. 30 felt can be expected to last a decade or more in good conditions. It's also easier to install for most roofers and less labor-intensive.

Felt is a good option for your roof if:

  • Your budget is tight.
  • You want an underlayment that is relatively fast and easy to install.
  • You know your roofer can complete your roofing job quickly and the felt won't be exposed to wind or rain.

However, if you have the budget and the time to install a synthetic underlayment, they are almost always worth the extra cost. Synthetic underlayments are lighter and more durable than felt, meaning you'll see less repair costs over time and less leaks or damage inside your home. Synthetic underlayment is also less likely to wrinkle or buckle underneath your shingle layer. However, synthetic underlayments do require more labor to install and carry a higher price tag than felt.

Synthetic underlayments are a good choice when:

  • The underlayment may be exposed to the elements for some time before the roof is complete.
  • You want the maximum amount of protection possible for your roof deck.
  • You have a lower-pitched roof that is more likely to have rain or ice intrude underneath the shingles.

Not sure which type of underlayment is right for you? Contact us today at Brax Roofing. We'll help you choose the right elements for your roof and get started on your project today.

 

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